Recently, techniques to display stereoscopic images with an image display device have been used. In the event of viewing such stereoscopic images displayed on an image display device, even when the angle of convergence is similar to the real world, focal distance may be different, becoming a factor causing visual fatigue. Particularly, in a case wherein a portion within the screen pops out excessively, or an object unnecessarily pops out during moving picture display and so forth, great visual changes are a burden to the viewer.
Therefore, conventionally, in order to perform natural stereoscopic displaying, a stereoscopic image display device has been proposed that displays so that the display position of the stereoscopic image is within the focal depth of the observer (for example, see PTL 1.). With this conventional stereoscopic image display device, the depth distance to be displayed is non-linearly converted to a depth distance of the display position of the stereoscopic image.